After weeks of dithering, Mali finally last week asked for United Nations backing in the hope of one day regaining control of the north of the country overrun six months ago by heavily armed Islamist groups. This initiative is supported by France.

Mali's decision opens the way for the deployment of five battalions – 3,300 combatants – provided by members of the Economic Community of West African States (Ecowas). Last Monday, on the sidelines of the UN general assembly meeting, the French foreign minister, Laurent Fabius, was finally able to announce that the interim president of Mali, Dioncounda Traoré, had asked UN secretary general Ban Ki-moon to table a security council resolution mandating an international force "to help the Malian army to reconquer the occupied areas of northern Mali".

Until recently Bamako had been keen to obtain outside help, but would not have foreign troops stationed in the capital. The government finally yielded to pressure from Ecowas, which is determined to prevent the rot spreading to neighbouring countries.

But the agreement underpinning intervention has yet to be finalised and much remains to be done. Ecowas is having difficulty finding troops, as potential participants have set stiff financial conditions. Many of their armies are already fully stretched.

There will be no lack of operational headaches. Bamako wants its own army to play a leading role, but it is currently in tatters after being mauled by a rebel offensive in mid-January. Some observers suggest it may take 18 months to put it back on its feet. Even with outside support it will be hard put to win back the northern provinces, held by some "6,000 Islamist combatants", according to a French estimate. So Mali and its neighbours are counting on various forms of support from further afield, mainly France: training, intelligence, cargo and combat aircraft.

At the UN general assembly last Wednesday, French president François Hollande called for a security council meeting "as soon as possible", but Paris is reluctant to be too active, for fear of being accused of neocolonialist intervention. It also wants to avoid exacerbating the plight of four French hostages held by al-Qaida in the Islamic Maghreb in northern Mali.

According to the International Crisis Group, the US is adopting a cautious stance, but Paris knows that US backing in the security council is vital. It will have to convince the Russians too. However, Britain is fully aware of the risks of regional instability and is particularly concerned about the threat to Nigeria and Sierra Leone posed by the proliferation of armed Islamist groups.